Semiconductor device and method for manuracturing the same

ABSTRACT

A semiconductor device of the present invention includes a gate electrode buried in a gate trench of a first conductivity-type semiconductor layer, a first conductivity-type source region, a second conductivity-type channel region, and a first conductivity-type drain region formed in the semiconductor layer, a second trench selectively formed in a source portion defined in a manner containing the source region in the surface of the semiconductor layer, a trench buried portion buried in the second trench, a second conductivity-type channel contact region selectively disposed at a position higher than that of a bottom portion of the second trench in the source portion, and electrically connected with the channel region, and a surface metal layer disposed on the source portion, and electrically connected to the source region and the channel contact region.

TECHNICAL FIELD

The present invention relates to a semiconductor device having atrench-gate structure and a method for manufacturing the same.

BACKGROUND ART

Semiconductor power devices have conventionally become the focus ofattention, which are mainly used for systems in various powerelectronics fields such as motor control systems and power conversionsystems.

As semiconductor power devices of this type, SiC semiconductor deviceshaving a trench-gate structure have been proposed, for example.

For example, Patent Literature 1 discloses a field effect transistorincluding an n⁺-type SiC substrate, an n⁻-type epitaxial layer (driftregion) formed on the SiC substrate, a p-type body region formed at asurface side of the epitaxial layer, an n⁺-type source region formed ata surface side within the body region, a grid-shaped gate trench formedin a manner penetrating through the source region and the body region toreach the drift region, a gate insulating film formed on the innersurface of the gate trench, a gate electrode embedded in the gatetrench, a source trench formed in a manner penetrating through thesource region and the body region to reach the drift region at aposition surrounded by the grid-shaped gate trench, and a sourceelectrode formed in a manner entering the source trench.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Publication No.    2011-134910

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to provide a semiconductordevice capable of improving the flatness of a surface metal layerwithout sacrificing conventional device performance and a method formanufacturing the same.

Solution to Problem

A semiconductor device of the present invention for achieving the aboveobject includes a semiconductor layer of a first conductivity typeformed with a gate trench, a gate electrode buried in the gate trenchvia a gate insulating film, a source region of a first conductivity typedisposed in a manner exposed on a surface of the semiconductor layer,forming a part of a side face of the gate trench, a channel region of asecond conductivity type disposed for the source region on a backsurface side of the semiconductor layer in a manner contacting thesource region, forming a part of the side face of the gate trench, adrain region of a first conductivity type disposed for the channelregion on the back surface side of the semiconductor layer in a mannercontacting the channel region, forming a bottom face of the gate trench,a second trench selectively formed in a source portion defined in amanner containing the source region in the surface of the semiconductorlayer, a trench buried portion buried in the second trench, a channelcontact region of a second conductivity type selectively disposed at aposition higher than that of a bottom portion of the second trench inthe source portion, electrically connected with the channel region, anda surface metal layer disposed on the source portion, electricallyconnected to the source region and the channel contact region.

According to this arrangement, because the trench buried portion isburied in the second trench, a difference in level (unevenness) betweenthe source portion and other parts can be reduced on the surface of thesemiconductor layer (device surface). The flatness of the surface metallayer on said device surface can thereby be improved. Thus, when, forexample, a wire is bonded to the surface metal layer, adhesion betweenthe surface metal layer and the wire can be improved. As a result, thewire can be satisfactorily bonded, so that the wire bonding portion canbe improved in reliability. Further, because the surface metal layer isexcellent in flatness, destruction of the device by ultrasonic vibrationand pressure can be prevented at the time of wire bonding, and a declinein assembling yield can be prevented.

On the other hand, a concentration of equipotential surfaces in thevicinity of a bottom portion of the gate trench can be prevented by thesecond trench, so that a potential gradient in the vicinity of thebottom port ion can be made gradual. Therefore, an electric fieldconcentration to the bottom portion of the gate trench can be relaxed.Further, because the channel contact region is disposed at a positionhigher than that of the bottom portion of the second trench, even whenthere is formed a second trench, contact with the channel region can bereliably made via the channel contact region. In other words, at thetime of an improvement in flatness of the surface metal layer, adegradation in device performance such as gate withstand voltage andcontact performance with the channel region can be prevented.

The semiconductor device of the present invention may further include asecond conductivity-type layer formed at the bottom portion and a sideportion of the second trench in a manner continuing from the channelregion and the channel contact region.

According to this arrangement, a depletion layer can be generated, by asecond conductivity-type layer different in conductivity type from thesemiconductor layer, from a junction (p-n junction) between said secondconductivity-type layer and the semiconductor layer. Moreover, becausethe depletion layer keeps equipotential surfaces away from the gatetrench, electric fields to be imposed on the bottom portion of the gatetrench can be further relaxed.

The trench buried portion may consist of an insulating film formed on aninner surface of the second trench and a polysilicon layer buried insideof the insulating film.

According to this arrangement, the polysilicon layer buried in thesecond trench can be used as an etching stopper, in the case where, forexample, there is formed a surface insulating film made of SiO₂ on thesurface of the semiconductor layer, when selectively etching the surfaceinsulating film to expose the source portion from a contact hole.Therefore, control of the step of said contact etching can be simplyperformed.

The insulating film may be made of any of SiO₂, AlON, Al₂O₃, SiO₂/AlON,SiO₂/AlON/SiO₂, SiO₂/SiN, and SiO₂/SiN/SiO₂.

According to this arrangement, by, for example, forming the gateinsulating film in the same step as that for the insulating film in thesecond trench, a gate insulating film constituted of a materialexemplified in the above can be provided. In this case, providing a gateinsulating film constituted of a high-dielectric-constant (high-k) filmof AlON, Al₂O₃, or the like allows an improvement in gate withstandvoltage, so that device reliability can be improved.

The insulating film may have a SiO₂ film containing nitrogen (N).

According to this arrangement, by, for example, forming the gateinsulating film in the same step as that for the insulating film in thesecond trench, a gate insulating film constituted of a material having aSiO₂ film containing nitrogen (N) can be provided. This gate insulatingfilm can improve channel mobility.

The insulating film may be, at the bottom portion of the second trench,formed to be thicker than a part at a side portion of the second trench.

According to this arrangement, by, for example, forming the gateinsulating film in the same step as that for the insulating film in thesecond trench, the gate insulting film can also be made, at the bottomportion of the gate trench, thicker than a part at a side portion of thegate trench. Withstand voltage in the bottom portion of the gate trenchcan thereby be improved.

The polysilicon layer may be made of n⁺-type polysilicon.

According to this arrangement, by, for example, forming the gateelectrode in the same step as that for the polysilicon layer in thesecond trench, a gate electrode constituted of n⁺-type polysilicon canbe provided. The n⁺-type polysilicon has a relatively low sheetresistance, which therefore allows increasing transistor switchingspeed.

The trench buried portion may consist of an insulating layer that fillsback the second trench.

According to this arrangement, because the inside of the second trenchis filled with the insulating layer, a leakage current that flows viathe second trench can be prevented or reduced.

The insulating layer may be made of SiO₂. In this case, the insulatinglayer may be made of SiO₂ containing phosphorus (P) or boron (B).

According to this arrangement, because the melting point of SiO₂ fallsas a result of containing phosphorous or boron, the process for buryingthe insulating film can be simply performed. As such SiO₂, for example,PSG (phosphorus silicate glass) or PBSG (phosphorus boron silicateglass) can be used.

The trench buried portion may consist of a polysilicon layer that fillsback the second trench.

According to this arrangement, the polysilicon layer buried in thesecond trench can be used as an etching stopper, in the case where, forexample, there is formed a surface insulating film made of SiO₂ on thesurface of the semiconductor layer, when selectively etching the surfaceinsulating film to expose the source portion from a contact hole.Therefore, control of the step of said contact etching can be simplyperformed.

The polysilicon layer may be made of p⁺-type polysilicon.

According to this arrangement, when, for example, the channel region andthe channel contact region are p-type, these regions can be electricallyconnected by use of a p⁺-type polysilicon layer. Because the length of acurrent path between the channel region and the channel contact regioncan thereby be reduced, a base resistance therebetween can be reduced.As a result, latch-up can be satisfactorily prevented. Further, when thechannel contact region is in contact with the polysilicon layer, acontact resistance therebetween can also be reduced. The reduction incontact resistance also contributes to a reduction in the baseresistance between the channel region and the channel contact region.

The gate electrode may be a metal gate electrode containing any of Mo,W, Al, Pt, Ni, and Ti.

According to this arrangement, gate resistance can be made relativelylow, which therefore allows increasing transistor switching speed.

The surface metal layer may be made of a metal containing copper (Cu).In this case, the surface metal layer may contain an Al—Cu-based alloy.

According to this arrangement, because the sheet resistance of thesurface metal layer can be reduced, the current density can beincreased.

The second trench may have an annular structure surrounding the channelcontact region.

The second trench may have a width the same as that of the gate trench.

According to this arrangement, when, for example, the gate trench andthe second trench are formed in the same step, the etching rate for thesecond trench can be made the same as that for the gate trench, so thatetching for forming the second trench can be stably controlled.

The semiconductor layer may have an active region that forms a channelin the channel region to perform a transistor operation and an outerperipheral region disposed around the active region, and thesemiconductor device may further include a surface insulating filmdisposed in a manner extending across the active region and the outerperipheral region, and in the active region, formed to be thinner than apart in the outer peripheral region. In this case, the surfaceinsulating film may have a thickness of 5000 Å or less in the activeregion.

Also, in the surface insulating film, a contact hole that selectivelyexposes the source portion may be formed over the entire surface of thesemiconductor layer.

In the semiconductor layer, a unit cell that forms a channel in thechannel region to perform a transistor operation may be defined in agrid shape by the gate trench. Or, in the semiconductor layer, a unitcell that forms a channel in the channel region to perform a transistoroperation may be defined in a striped shape by the gate trench.

The semiconductor layer may be made of SiC, GaN, or diamond.

A method for manufacturing a semiconductor device of the presentinvention includes a step of simultaneously forming, in a semiconductorlayer formed with a source region of a first conductivity type, achannel region of a second conductivity type, and a drain region of afirst conductivity type in order from a surface side to a back surfaceside in a manner contacting each other, a gate trench and a secondtrench that penetrate through the source region and the channel regionfrom the surface to reach the drain region, a step of selectivelyforming a channel contact region of a second conductivity type to beelectrically connected with the channel region, at a position higherthan that of a bottom portion of the second trench in the semiconductorlayer, a step of burying a gate electrode via a gate insulating film inthe gate trench, a step of burying a trench buried portion in the secondtrench, a step of selectively exposing a source portion containing thesource region, the channel contact region, and the trench buried portion in the surface of the semiconductor layer, and selectively coveringa part other than the source portion, and a step of forming, on thesource portion, a surface metal layer to be electrically connected tothe source region and the channel contact region.

According to this method, because a semiconductor device of the presentinvention can be manufactured, a semiconductor device capable ofimproving the flatness of a surface metal layer without sacrificingconventional device performance can be provided.

Also, because the second trench is formed simultaneously with the gatetrench, the second trench can be simply formed free from misalignment,without increasing the manufacturing process.

The method of the semiconductor device of the present invention mayfurther include a step of forming a second conductivity-type layer atthe bottom portion and a side portion of the second trench in a mannercontinuing from the channel region and the channel contact region.

According to this method, a depletion layer can be generated, by asecond conductivity-type layer different in conductivity type from thesemiconductor layer, from a junction (p-n junction) between said secondconductivity-type layer and the semiconductor layer. Moreover, becausethe depletion layer keeps equipotential surfaces away from the gatetrench, electric fields to be imposed on the bottom portion of the gatetrench can be further relaxed.

The step of burying the trench buried portion may include a step offorming an insulating film on an inner surface of the second trench andthen burying a polysilicon layer inside of the insulating film.

According to this method, the polysilicon layer buried in the secondtrench can be used as an etching stopper, in the case where, forexample, a surface insulating film made of SiO₂ is formed on the surfaceof the semiconductor layer, when selectively etching the surfaceinsulating film to expose the source portion from a contact hole.Therefore, control of the step of said contact etching can be simplyperformed.

The step of burying the trench buried portion may include a step offilling back the second trench with an insulating layer.

According to this method, because of filling the inside of the secondtrench with the insulating layer, a semiconductor device capable ofpreventing or reducing a leakage current that flows via the secondtrench can be provided.

The step of burying the trench buried portion may include a step offilling back the second trench with a polysilicon layer.

According to this method, the polysilicon layer buried in the secondtrench can be used as an etching stopper, in the case where, forexample, a surface insulating film made of SiO₂ is formed on the surfaceof the semiconductor layer, when selectively etching the surfaceinsulating film to expose the source portion from a contact hole.Therefore, control of the step of said contact etching can be simplyperformed.

The step of forming the gate trench and the second trench may include astep of forming a gate trench and a second trench being the same widthas each other.

According to this method, the etching rate for the second trench can bemade the same as that for the gate trench, so that etching for formingthe second trench can be stably controlled.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are a schematic plan view of a semiconductor deviceaccording to a first preferred embodiment of the present invention, inwhich FIG. 1 (a) shows an overall view and FIG. 1 (b) shows a layoutdiagram of a plurality of unit cells.

FIG. 2 is an enlarged view showing a main part of the semiconductordevice according to the first preferred embodiment of the presentinvention, in which an upper side of the figure shows a sectional viewand a lower side of the figure shows a plan view.

FIG. 3A is a schematic view showing a part of a process formanufacturing the semiconductor device according to the first preferredembodiment of the present invention.

FIG. 3B is a view showing a step following that of FIG. 3A.

FIG. 3C is a view showing a step following that of FIG. 3B.

FIG. 3D is a view showing a step following that of FIG. 3C.

FIG. 3E is a view showing a step following that of FIG. 3D.

FIG. 3F is a view showing a step following that of FIG. 3E.

FIG. 3G is a view showing a step following that of FIG. 3F.

FIG. 3H is a view showing a step following that of FIG. 3G.

FIG. 3I is a view showing a step following that of FIG. 3H.

FIG. 3J is a view showing a step following that of FIG. 3I.

FIG. 3K is a view showing a step following that of FIG. 3J.

FIG. 4 is an enlarged view showing a main part of a semiconductor deviceaccording to a second preferred embodiment of the present invention, inwhich an upper side of the figure shows a sectional view and a lowerside of the figure shows a plan view.

FIG. 5A is a schematic view showing apart of a process for manufacturingthe semiconductor device according to the second preferred embodiment ofthe present invention.

FIG. 5B is a view showing a step following that of FIG. 5A.

FIG. 6 is an enlarged view showing a main part of a semiconductor deviceaccording to a third preferred embodiment of the present invention, inwhich an upper side of the figure shows a sectional view and a lowerside of the figure shows a plan view.

FIG. 7A is a schematic view showing a part of a process formanufacturing the semiconductor device according to the third preferredembodiment of the present invention.

FIG. 7B is a view showing a step following that of FIG. 7A.

FIG. 8 is a view showing a modification of the layout of unit cells.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bespecifically described with reference to the drawings.

First Preferred Embodiment

FIGS. 1(a) and 1(b) are a schematic plan view of a semiconductor deviceaccording to a first preferred embodiment of the present invention, inwhich FIG. 1 (a) shows an overall view and FIG. 1(b) shows a layoutdiagram of a plurality of unit cells.

The semiconductor device 1 includes a SiC-based trench-gate type MISFET(Metal Insulator Semiconductor Field Effect Transistor). As shown inFIG. 1 (a), the semiconductor device 1 has, for example, a squarechip-shaped contour in a plan view. The chip-shaped semiconductor device1 is sized to have a vertical and horizontal length of about severalmillimeters in the illustration of FIG. 1 (a). An active region 2 and anouter peripheral region 3 disposed around the active region 2 are set ona surface of the semiconductor device 1.

In the active region 2, a plurality of unit cells 4 each of whichperforms a transistor operation are defined in a grid shape by a gatetrench 5. Each unit cell 4 includes an annular n⁺-type source region 6,an annular source trench 7 (second trench) surrounded by the n⁺-typesource region 6, and a p⁺-type channel contact region 8 formed in anisland shape inside the source trench 7. The p⁺-type channel contactregion 8 is surrounded by the source trench 7 at its periphery. Also,each unit cell 4 is sized to have a vertical and horizontal length ofabout 10 μm in the illustration of FIG. 1 (b).

The outer peripheral region 3 is, in the present preferred embodiment,formed in an annular shape in a manner surrounding the active region 2.In the outer peripheral region 3, a plurality of guard rings 9 areformed spaced apart from each other, in a manner surrounding the activeregion 2. In addition, the guard rings 9 under a source pad 10(described later) are shown perspectively in FIG. 1 (a).

A source pad 10 (surface metal layer) is formed on the surface of thesemiconductor device 1. The source pad 10 is formed across substantiallythe whole of the surface of the semiconductor device 1, in a mannerextending across the plurality of unit cells 4. The source pad 2, in thepresent preferred embodiment, has a substantially square shape in a planview with the four corners being curved outward. A removal region 11 isformed near the center of one side of the source pad 10. The removalregion 11 is a region in which the source pad 10 is not formed.

Agate pad 12 is disposed in the removal region 11. The gate pad 12 andthe source pad 10 are provided with an interval therebetween, and areinsulated from each other.

FIG. 2 is an enlarged view showing a main part of the semiconductordevice according to the first preferred embodiment of the presentinvention, in which an upper side of the figure shows a sectional view,and a lower side of the figure shows a plan view.

Next, an internal structure of the semiconductor device 1 will bedescribed.

The semiconductor device 1 includes a substrate (not shown) made ofn⁺-type SiC (for example, having a concentration of 1×10¹⁸ to 1×10²¹cm⁻³) and an n⁻-type epitaxial layer 13 made of n⁻-type SiC (forexample, having a concentration of 1×10¹⁵ to 1×10¹⁷ cm⁻³) formed on thesubstrate. The n⁻-type epitaxial layer 13 is a layer formed by causingSiC to epitaxially grow on a surface of the substrate. In the presentpreferred embodiment, the substrate and the n⁻-type epitaxial layer 13are shown as an example of a semiconductor layer of the presentinvention.

In a surface portion of the n⁻-type epitaxial layer 13, a p-type well 14(for example, having a concentration of 1×10¹⁶ to 1×10¹⁹ cm⁻³) is formedin a manner extending across the active region 2 and the outerperipheral region 3. On the other hand, a region of a portion under thep-type well 14 in the n⁻-type epitaxial layer 13 is an n⁻-type drainregion 15.

An n⁺-type source region 6 is formed in a surface portion of the p-typewell 14 in the active region 2, and exposed on the surface of then⁻-type epitaxial layer 13. In addition, the part of the p-type well 14within the active region 2 is a p-type channel region 16 which isdisposed in a manner contacting the n⁺-type source region 6 and in whicha channel is formed at the time of a transistor operation.

Moreover, the gate trench 5 and the source trench 7 are formed in amanner penetrating through the n⁺-type source region 6 and the p-typechannel region 16 (p-type well 14) to reach the n⁻-type drain region 15.The gate trench 5 and the source trench 7 are, in the present preferredembodiment, formed with the same width and the same depth, but may bedifferent in depth from each other. For example, the source trench 7 maybe shallower or may be deeper than the gate trench 5.

Each unit cell 4 is separated into a prismatic portion 17 surrounded bythe source trench 7 and an annular portion 18 disposed between thesource trench 7 and the gate trench 5 and spaced apart from theprismatic portion 17 by the source trench 7. In the present preferredembodiment, the width W₁ of the annular portion 18 (distance between thesource trench 7 and the gate trench 5) is, for example, 0.5 μm to 2.0μm.

In a top portion of the prismatic portion 17, a p⁺-type channel contactregion 8 (for example, having a concentration of 1×10¹⁸ to 1×10²¹ cm⁻³)is formed in a manner exposed on the surface of the n⁻-type epitaxiallayer 13. Accordingly, the p⁺-type channel contact region 8 forms a partof the side face of the source trench 7. The p⁺-type channel contactregion 8, in the present preferred embodiment, has its deepest portionat a position higher than that of a bottom portion of the source trench7, but the deepest portion is not particularly necessary at thisposition. As long as an uppermost portion of the p⁺-type channel contactregion 8 (in the present preferred embodiment, the part exposed on thesurface of the n⁻-type epitaxial layer 13) is at a position higher thanthat of the bottom portion of the source trench 7 and is contactable,said deepest portion may be at the same depth position as that of thebottom portion of the source trench 7 or may be deeper.

In the annular portion 18, an n⁺-type source region 6 and a p-typechannel region 16 are formed in order from the surface side.Accordingly, the n⁺-type source region 6 and the p-type channel region16 form parts of the side face of the gate trench 5, respectively. Then⁺-type source region 6 is, in the present preferred embodiment, formedwith the same depth as that of the p⁺-type channel contact region 8.

Also, in the n⁻-type epitaxial layer 13, a p-type layer 19 (for example,having a concentration of 1×10¹⁶ to 1×10¹⁹ cm⁻³) serving as an exampleof a second conductivity-type layer of the present invention is formedin a manner continuing from the p-type channel region 16 and the p⁺-typechannel contact region 8. The p-type layer 19 is, in the presentpreferred embodiment, formed in a manner extending across the prismaticportion 17 and the annular portion 18 via the bottom portion of thesource trench 7, and its inner region is in contact with the sourcetrench 7 (exposed into the source trench 7). The p-type layer 19 isconnected to the p-type channel region 16 at a portion lateral to thesource trench 7 of the annular portion 18, and is connected to thep⁺-type channel contact region 8 at a portion lateral to the sourcetrench 7 of the prismatic portion 17. Thus, the p-type channel region 16and the p⁺-type channel contact region 8 are electrically connected viathe p-type layer 19.

Also, the p-type layer 19 is also formed in a manner extending acrossouter peripheral edges of the gate trench 5 via a bottom portion of anoutermost peripheral line of the gate trench 5, and is connected, at theouter peripheral edges, to the p-type well 14 extending to the outerperipheral region 3.

Also, the p-type layer 19 is, at the bottom portion of the source trench7, formed to be thicker than a part at a side portion of the sourcetrench 7. However, in the prismatic portion 17, a portion lateral to thesource trench 7 is surrounded by the source trench 7, and ionimplantation is uniformly performed from its periphery. Therefore, thep-type layer 19 is formed thicker than the part at the bottom portion ofthe source trench 7, so as to fill a part under the p⁺-type channelcontact region 8.

Also, the p-type layer 19 is formed in a manner extending along the gatetrench 5. In the present preferred embodiment, the p-type layer 19 isformed across the entire periphery of the annular portion 18 surroundedby the gate trench 5, in a manner not contacting the gate trench 5(spaced from the gate trench 5). Accordingly, an n⁻-type drain region 15is disposed at a part of the side face of the gate trench 5, so that acurrent path at the time of channel formation can be secured.

The gate trench 5 is, in the present preferred embodiment, formed in asubstantially U-shape in a sectional view having a side face and abottom face. On an inner surface (side face and bottom face) of the gatetrench 5, a gate insulating film 20 is formed such that its one surfaceand the other surface extend along the inner surface of the gate trench5.

The gate insulating film 20 is, at the bottom portion of the gate trench5, formed to be thicker than a part at a side portion of the gate trench5. In the gate trench 5 having a substantially U-shape in a sectionalview as in the present preferred embodiment, the relatively thick partof the gate insulating film 20 is a part that contacts the bottom faceof the gate trench 5, and the relatively thin part is a part thatcontacts the side face of the gate trench 5. By making the insulatingfilm thick at the bottom portion of the gate trench 5 where electricfield concentration is likely to occur, withstand voltage in the bottomportion of the gate trench 5 can be improved. In addition, the side faceand bottom face sometimes cannot be clearly distinguished depending onthe shape of the gate trench 5, but in that case, it suffices that thegate insulating film 20 that contacts a face in a direction crossing thedepth direction of the gate trench 5 is relatively thick.

Moreover, the inside of the gate insulating film 20 is filled back witha gate electrode 21. In the present preferred embodiment, the gateelectrode 21 is buried in the gate trench 5 such that its upper facebecomes substantially flush with the surface of the n⁻-type epitaxiallayer 13. The gate electrode 21 is opposed to the p-type channel region16 via the gate insulating film 20. In each unit cell 4, by controllinga voltage to be applied to the gate electrode 21, an annular channelalong the periphery of the unit cell 4 is formed in the p-type channelregion 16. Then, a drain current that flows along the side face of thegate trench 5 toward the surface of the n⁻-type epitaxial layer 13 canbe caused to flow to the n⁺-type source region 6 via the channel. Atransistor operation of the semiconductor device 1 is thereby performed.

Similarly, the source trench 7 is also, in the present preferredembodiment, formed in a substantially U-shape in a sectional view havinga side face and a bottom face. On an inner surface (side face and bottomface) of the source trench 7, a source trench insulating film 22 isformed such that its one surface and the other surface extend along theinner surface of the source trench 7.

The source trench insulating film 22 is, at the bottom portion of thesource trench 7, formed to be thicker than a part at a side portion ofthe source trench 7. In addition, the side face and bottom facesometimes cannot be clearly distinguished depending on the shape of thesource trench 7, but in that case, it suffices that the source trenchinsulating film 22 that contacts a face in a direction crossing thedepth direction of the source trench 7 is relatively thick. Moreover,the inside of the source trench insulating film 22 is filled back with atrench buried layer 23. In the present preferred embodiment, the trenchburied layer 23 is buried in the source trench 7 such that its upperface becomes substantially flush with the surface of the n⁻-typeepitaxial layer 13.

In the present preferred embodiment, the gate insulating film 20 and thesource trench insulating film 22 are constituted of the same material,and the gate electrode 21 and the trench buried layer 23 are constitutedof the same material.

For example, as the material for the gate insulating film 20 and thesource trench insulating film 22, a film of any of SiO₂, AlON, Al₂O₃,SiO₂/AlON, SiO₂/AlON/SiO₂, SiO₂/SiN, and SiO₂/SiN/SiO₂ can be used, andmore preferably, a film having a SiO₂ film containing nitrogen (N) isused. In addition, SiO₂/AlON means a laminated film of SiO₂ (lower side)and AlON (upper side). Providing a gate insulating film 20 constitutedof a high-dielectric-constant (high-k) film of AlON, Al₂O₃, or the likeallows an improvement in gate withstand voltage, so that devicereliability can be improved. Further, providing a gate insulating film20 constituted of a material having a SiO₂ film containing nitrogen (N)also allows an improvement in channel mobility.

As the material for the gate electrode 21 and the trench buried layer23, polysilicon can be used, and more preferably, n⁺-type polysilicon isused. The n⁺-type polysilicon has a relatively low sheet resistance,which therefore allows increasing transistor switching speed.

In addition, the gate insulating film 20 and the source trenchinsulating film 22 may be constituted of materials different from eachother. Similarly, the gate electrode 21 and the trench buried layer 23may also be constituted of materials different from each other. Forexample, the gate electrode 21 may be a metal gate electrode containingany of Mo, W, Al, Pt, Ni, and Ti. The metal gate electrode can also makegate resistance relatively low, which therefore allows increasingtransistor switching speed.

In a surface portion of the p-type well 14 in the outer peripheralregion 3, a p⁺-type well contact region 24 (for example, having aconcentration of 1×10¹⁸ to 1×10²¹ cm⁻³) is formed. The p⁺-type wellcontact region 24 is, in the present preferred embodiment, in an annularshape in a manner surrounding the active region 2, and is formed withthe same depth as that of the p⁺-type channel contact region 8.

Also, outside of the p-type well 14 in the outer peripheral region 3,guard rings 9 are formed spaced from the p-type well 14.

The guard ring 9, in the present preferred embodiment, includes a trench31 formed in the surface of the n⁻-type epitaxial layer 13 and a p-typelayer 32 (for example, having a concentration of 1×10¹⁶ to 1×10¹⁹ cm⁻³)formed at, at least, a bottom portion of the trench 31. In the presentpreferred embodiment, the p-type layer 32 is formed at bottom and sideportions of the trench 31, and is, at the bottom portion of the trench31, formed to be thicker than a part at the side portion of the trench31. Also, in the present preferred embodiment, the trench 31 is formedwith the same depth as that of the gate trench 5, and the p-type layer32 is formed with the same depth as that of the p-type layer 19.

Similar to the gate trench 5, in the trench 31, a trench buried layer 34is buried via a trench insulating film 33. As the materials for thetrench insulating film 33 and the trench buried layer 34, the samematerials as those for the gate insulating film 20 and the gateelectrode 21 can be used, respectively.

On the surface of the n⁻-type epitaxial layer 13, a surface insulatingfilm 25 is formed so as to extend across the active region 2 and theouter peripheral region 3. The surface insulating film 25 is made of aninsulator such as silicon oxide (SiO₂), for example. The surfaceinsulating film 25 is formed such that an inner part 27 on the activeregion 2 becomes thinner than an outer part 26 on the outer peripheralregion 3. In the present preferred embodiment, the inner part 27 on theactive region 2 has a thickness of 5000 Å or less, and the outer part 26on the outer peripheral region 3 has a thickness of about 5500 Å to20000 Å. The surface insulating film 25 may be called an interlayerinsulating film when a multilayer wiring structure is disposed thereon,which is not shown in FIG. 2.

In the surface insulating film 25, contact holes 28 that selectivelyexpose the p⁺-type channel contact region 8, the source trench 7, andthe n⁺-type source region 6 are formed for every unit cell 4 over theentire surface of the n⁻-type epitaxial layer 13. In the presentpreferred embodiment, a source portion 30 is defined in each unit cell 4by the contact hole 28. Also, in the surface insulating film 25, acontact hole 29 that selectively exposes the p⁺-type well contact region24 is formed over the entire surface of the n⁻-type epitaxial layer 13.

On the surface insulating film 25, a source pad 10 is formed. The sourcepad 10 is connected collectively to the p⁺-type channel contact regions8 and the n⁺-type source regions 6 of all unit cells 4 and the p⁺-typewell contact region 24 via the respective contact holes 28 and 29. Inother words, the source pad 10 serves as a common electrode to all unitcells 4. Also, as the material for the source pad 10, a metal containingcopper (Cu) may be used, and more preferably, a metal containing anAl—Cu-based alloy is used. Because the sheet resistance of the sourcepad 10 can thereby be reduced, the current density can be increased.Also, the source pad 10 has a thickness (distance from the surface ofthe n⁻-type epitaxial layer 13 to a surface of the source pad 10) of,for example, 4 μm to 5 μm. In addition, the source pad 10 may have acontact metal made of, for example, a laminated structure (Ti/TiN) oftitanium (Ti) and titanium nitride (TiN) at a connection part with then⁻-type epitaxial layer 13.

On the other hand, the gate pad 12 (refer to FIG. 1(a)) is electricallyconnected to the gate electrode 21 via a gate wiring (not shown) or thelike.

FIG. 3A to FIG. 3K are schematic views showing in the order of steps apart of a process for manufacturing the semiconductor device accordingto the first preferred embodiment of the present invention.

For manufacturing the semiconductor device 1, as shown in FIG. 3A, ann-type impurity is doped into the surface of a SiC substrate (not shown)while SiC crystals are caused to grow thereon by epitaxy such as a CVDmethod, an LPE method, or an MBE method. An n⁻-type epitaxial layer 13is thereby formed on the SiC substrate. In addition, as the n-typeimpurity, for example, N (nitride), P (phosphorous), As (arsenic), orthe like can be used.

Next, a p-type impurity is selectively ion-implanted from the surface ofthe n⁻-type epitaxial layer 13. A p-type well 14 (p-type channel region16) is thereby formed. In addition, as the p-type impurity, for example,Al (aluminum), B (boron), or the like can be used. Also, simultaneouslywith formation of the p-type well 14, the rest of the n⁻-type epitaxiallayer 13 is formed as an n⁻-type drain region 15.

Next, as shown in FIG. 3B, an n-type impurity is selectivelyion-implanted from the surface of the n⁻-type epitaxial layer 13. Ann⁺-type source region 6 is thereby formed.

Next, as shown in FIG. 3C, the n⁻-type epitaxial layer 13 is selectivelyetched by use of a mask having openings in regions where the gate trench5, the source trenches 7, and the trenches 31 are to be formed. Ann⁻-type epitaxial layer 13 is thereby dry-etched from the surface in amanner penetrating through the n⁺-type source region 6 and the p-typechannel region 16, so that a gate trench 5, source trenches 7, andtrenches 31 are simultaneously formed. In conjunction therewith, then⁻-type epitaxial layer 13 is defined into a plurality of unit cells 4by the gate trench 5. The unit cells 4 are to have prismatic portions 17and annular portions 18. Also, as an etching gas, for example, a mixedgas (SF₆/O₂ gas) containing SF₆ (sulfur hexafluoride) and O₂ (oxygen), amixed gas (SF₆/O₂/HBr gas) containing SF₆, O₂, and HBr (hydrogenbromide), or the like can be used.

Next, as shown in FIG. 3D, a p-type impurity is selectivelyion-implanted from the surface of the n⁻-type epitaxial layer 13. Thep-type impurity is implanted, for example, in a direction perpendicularto the surface of the n⁻-type epitaxial layer 13. A p-type layer 19 anda p-type layer 32 are thereby simultaneously formed. In addition, thep-type layer 19 and the p-type layer 32 may be formed by separate ionimplantation steps.

Next, as shown in FIG. 3E, a p-type impurity is selectivelyion-implanted from the surface of the n⁻-type epitaxial layer 13.P⁺-type channel contact regions 8 and a p⁺-type well contact region 24are thereby simultaneously formed.

Next, the n⁻-type epitaxial layer 13 is thermally treated at 1400° C. to2000° C., for example. The ions of the p-type impurity and n-typeimpurity implanted into the n⁻-type epitaxial layer 13 are therebyactivated.

Next, as shown in FIG. 3F, a gate insulating film 20, a source trenchinsulating film 22, and a trench insulating film 33 are simultaneouslyformed by, for example, thermal oxidization. In addition, when the gateinsulating film 20, the source trench insulating film 22, and the trenchinsulating film 33 are constituted of high-dielectric-constant (high-k)films, it suffices to deposit a film material by a CVD method.

Next, as shown in FIG. 3G, a polysilicon material doped with an n-typeimpurity is deposited from above the n⁻-type epitaxial layer 13 by, forexample, a CVD method. The deposition of the polysilicon material iscontinued until at least the gate trench 5, the source trenches 7, andthe trenches 31 have been completely filled back. Thereafter, thedeposited polysilicon material is etched back until its etched-back facebecomes flush with the surface of the n⁻-type epitaxial layer 13. A gateelectrode 21 and trench buried layers 23 and 34 are therebysimultaneously formed.

Next, as shown in FIG. 3H, an insulating material such as SiO₂ isdeposited from above the n⁻-type epitaxial layer 13 by, for example, aCVD method. A surface insulating film 25 is thereby formed.

Next, as shown in FIG. 3I, a part on the active region 2 of the surfaceinsulating film 25 is selectively etched. Only said part is therebythinned, so that an inner part 27 and an outer pert 26 of the surfaceinsulating film 25 are formed.

Next, as shown in FIG. 3J, by the surface insulating film 25 beingselectively etched, contact holes 28 and 29 are simultaneously formed.

Next, as shown in FIG. 3K, a metal material is deposited from above then⁻-type epitaxial layer 13 by, for example, a sputtering method. Then,by patterning said material, a source pad 10 is formed. Thesemiconductor device 1 shown in FIG. 2 is obtained through the abovesteps.

As above, according to the present semiconductor device 1, the trenchburied layer 23 is buried in the source trenches 7 via the trenchinsulating film 22. Therefore, on the surface of the n⁻-type epitaxiallayer 13 (device surface), a difference in level (unevenness) betweenthe source portions 30 exposed from the contact holes 28 and other partscan be reduced. The flatness of the source pad 10 on said device surfacecan thereby be improved. Thus, when, for example, a wire is bonded tothe surface of the source pad 10, adhesion between the source pad 10 andthe wire can be improved. As a result, the wire can be satisfactorilybonded, so that the wire bonding portion can be improved in reliability.Further, because the source pad 10 is excellent in flatness, destructionof the device by ultrasonic vibration and pressure can be prevented atthe time of wire bonding, and a decline in assembling yield can beprevented.

On the other hand, a concentration of equipotential surfaces in avicinity of the bottom portion of the gate trench 5 can be prevented bythe source trench 7, so that a potential gradient in the vicinity of thebottom port ion can be made gradual. Therefore, an electric fieldconcentration to the bottom portion of the gate trench 5 can be relaxed.Further, the p⁺-type channel contact region 8 is formed in the topportion of the prismatic portion 17 and is disposed at a position higherthan that of the bottom portion of the source trench 7. Thus, even whenthere is formed a source trench 7, contact with the p-type channelregion 16 can be reliably made via the p⁺-type channel contact region 8.In other words, at the time of an improvement in flatness of the sourcepad 10, a degradation in device performance such as gate withstandvoltage and contact performance with the p-type channel region 16 can beprevented.

Further, in the present preferred embodiment, because the p-type layer19 is formed around the source trench 7, a depletion layer can begenerated from a junction (p-n junction) between the p-type layer 19 andthe n⁻-type drain region 15. Moreover, because the depletion layer keepsequipotential surfaces away from the gate trench 5, electric fields tobe imposed on the bottom portion of the gate trench 5 can be furtherrelaxed.

Also, in the present preferred embodiment, because a SiC device in whichlatch-up is unlikely to occur as compared with a Si device is used, thep⁺-type channel contact region 8 and the p-type channel region 16 can beprovided at positions separated from each other by the source trench 7.That is, in a Si device, because latch-up is relatively likely to occur,it is preferable to dispose the p⁺-type channel contact region 8 nearthe p-type channel region 16 to reduce the distance between the regions8 and 16 as short as possible so as to lower a base resistance betweensaid regions 8 and 16. On the other hand, in such a SiC device as thepresent semiconductor device 1, because latch-up is relatively unlikelyto occur and the importance of considering a base resistance between theregions 8 and 16 is low, the p⁺-type channel contact region 8 does notneed to be disposed near the p-type channel region 16. Thus, the p⁺-typechannel contact region 8 and the p-type channel region 16 can beprovided at positions separated from each other by the source trench 7to electrically connect the regions 8 and 16 by a route through thebottom portion of the source trench 7.

Also, because the source trench insulating film 22 is disposed outsideof the trench buried layer 23, flow of an off-leakage current betweenthe n⁻-type epitaxial layer 13 and the source pad 10 can be prevented.Specifically, the p-type layer 19 is, at a side portion of the sourcetrench 7, thinner than a part at the bottom portion of the source trench7 because ions are unlikely to enter a portion lateral to the sourcetrench 7 at the time of ion implantation. Therefore, when a high voltageis applied at OFF-time, an off-leakage current may flow passing throughthe thin part of the p-type layer 19. Therefore, forming a source trenchinsulating film 22 allows reliably interrupting a leakage current by thesource trench insulating film 22 even if an off-leakage current passesthrough the p-type layer 19.

Also, if the trench buried layer 23 buried in the source trench 7 ispolysilicon, when forming contact holes 28 in the surface insulatingfilm 25 made of SiO₂ (FIG. 3J), the trench buried layer 23 (polysiliconlayer) can be used as an etching stopper. Therefore, control of the stepof said contact etching can be simply performed.

Also, because the source trenches 7 are formed simultaneously with thegate trench 5 (FIG. 3C), the source trenches 7 can be simply formedwithout increasing the manufacturing process. Further, if the sourcetrenches 7 and the gate trench 5 are the same width, the etching ratefor the source trenches 7 can be made the same as that for the gatetrench 5, so that etching for forming the source trenches 7 can bestably controlled.

Second Preferred Embodiment

FIG. 4 is an enlarged view showing a main part of a semiconductor deviceaccording to a second preferred embodiment of the present invention, inwhich an upper side of the figure shows a sectional view, and a lowerside of the figure shows a plan view. In FIG. 4, parts corresponding tothe respective portions shown in FIG. 1 and FIG. 2 described above areshown with the same reference signs.

In the first preferred embodiment described above, the trench buriedportion buried in the source trench 7 consists of the source trenchinsulating film 22 and the trench buried layer 23 (polysilicon layer),but as in the present semiconductor device 41, it may consist only of aninsulating layer 42 that fills back the source trenches 7.

As the material for the insulating layer 42, SiO₂ can be used, and morepreferably, SiO₂ containing phosphorus (P) or boron (B) is used. As suchSiO₂, for example, PSG (phosphorus silicate glass) or PBSG (phosphorusboron silicate glass) can be used.

A process for manufacturing the semiconductor device 41 according to thepresent preferred embodiment is substantially the same as the stepsshown in FIG. 3A to FIG. 3K. However, after a gate electrode 21 andtrench buried layers 23 and 34 are formed in the step of FIG. 3G, asshown in FIG. 5A, the trench buried layer 23 is selectively etched to beremoved, so that the source trenches 7 are made hollow. Then, as shownin FIG. 5B, a surface insulating film 25 is formed on the n⁻-typeepitaxial layer 13 to thereby fill back the source trenches 7 by use ofapart of the surface insulating film 25. The source trench insulatingfilm 22 and the surface insulating film 25 are thereby integrated insidethe source trenches 7, so that an insulating layer 42 is formed.

According to the present semiconductor device 41, because the sourcetrenches 7 are filled with the insulating layer 42, flow of anoff-leakage current between the n⁻-type epitaxial layer 13 and thesource pad 10 can be effectively prevented.

Also, if the insulating layer 42 is SiO₂ containing phosphorous orboron, because the melting point of SiO₂ falls, the process for buryingthe insulating layer 42 can be simply performed.

Of course, in the present semiconductor device 41 as well, the sameeffects as those of the first preferred embodiment can also be realized.

Third Preferred Embodiment

FIG. 6 is an enlarged view showing a main part of a semiconductor deviceaccording to a third preferred embodiment of the present invention, inwhich an upper side of the figure shows a sectional view, and a lowerside of the figure shows a plan view. In FIG. 6, parts corresponding tothe respective portions shown in FIG. 1 and FIG. 2 described above areshown with the same reference signs.

In the first preferred embodiment described above, the trench fillingportion buried in the source trench 7 consists of the source trenchinsulating film 22 and the trench buried layer 23 (polysilicon layer),but as in the present semiconductor device 61, it may consist only of apolysilicon layer 62 that fills back the source trenches 7. As thematerial for the polysilicon layer 62, p⁺-type polysilicon is preferablyused.

A process for manufacturing the semiconductor device 61 according to thepresent preferred embodiment is substantially the same as the stepsshown in FIG. 3A to FIG. 3K. However, after a gate insulating film 20, asource trench insulating film 22, and a trench insulating film 33 areformed in the step of FIG. 3F, as shown in FIG. 7A, the source trenchinsulating film 22 is selectively etched to be removed, so that thesource trenches 7 are made hollow. Then, as shown in FIG. 7B, bypolysilicon being deposited from above the n⁻-type epitaxial layer 13,the source trenches 7 are filled back with that polysilicon. A gateelectrode 21 and a polysilicon layer 62 are thereby simultaneouslyformed.

According to the present semiconductor device 61, because thepolysilicon layer 62 is buried in the source trenches 7, when formingcontact holes 28 in the surface insulating film 25 made of SiO₂ (FIG.3J), the polysilicon layer 62 can be used as an etching stopper.Therefore, control of the step of said contact etching can be simplyperformed.

Also, if the polysilicon layer 62 is p⁺-type polysilicon, the p⁺-typechannel contact region 8 and the p-type channel region 16 can beelectrically connected by use of the polysilicon layer 62. Because thelength of a current path between the regions 8 and 16 can thereby bereduced, a base resistance therebetween can be reduced. As a result,latch-up can be satisfactorily prevented. Further, because the p⁺-typechannel contact region 8 is in contact with the polysilicon layer 62 ata side face of the source trench 7, a contact resistance therebetweencan also be reduced. The reduction in contact resistance alsocontributes to a reduction in the base resistance between the regions 8and 16.

Of course, in the present semiconductor device 61 as well, the sameeffects as those of the first preferred embodiment can also be realized.

Although preferred embodiments of the present invention have beendescribed above, the present invention can be embodied in other forms.

For example, an arrangement may be adopted in which the conductivitytype of each semiconductor part of each semiconductor device (1, 41, 61)is inverted. For example, in the semiconductor devices 1, the p-typeparts may be n-type and the n-type parts may be p-type.

Also, in the semiconductor device (1, 41, 61), the layer thatconstitutes a semiconductor layer is not limited to an n⁻-type epitaxiallayer made of SiC, and may be a layer or the like made of GaN, diamond,or Si.

Also, each unit cell 4 is not limited to a square shape in a plan view(quadrangular shape), but may have another shape such as, for example, atriangular shape in a plan view, a pentagonal shape in a plan view, or ahexagonal shape in a plan view, and may further have a stripe shape asin the semiconductor device 81 of FIG. 8.

Also, in the preferred embodiment described above, an example has beenmentioned in which the source trench 7 is formed in an annular shape andthe channel contact region 8 is disposed inside thereof, but the sourcetrench 7 need not to be an annular shape. For example, the source trench7 may be formed in a recessed shape such as a triangle, quadrangle,circle, or oblong in a plan view and the channel contact region 8 may bedisposed outside thereof.

Also, the guard ring 9 is a structure including the trench 31 formed inthe surface of n⁻-type epitaxial layer 13 and the p-type layer 32 formedin, at least, the bottom portion of the trench 31, but may be astructure consisting only of, for example, p-type semiconductor regions.

The semiconductor device of the present invention can be incorporatedin, for example, a power module for use in an inverter circuit thatconstitutes a drive circuit for driving an electric motor available as apower source for an electric vehicle (including a hybrid vehicle), anelectric train, an industrial robot, and the like. Additionally, thesemiconductor device of the present invention can also be incorporatedin a power module for use in an inverter circuit that converts electricpower generated by a solar cell, a wind power generator, and other powergenerators (particularly, private electric generators) so as to bematched with electric power from commercial power sources.

Also, the features grasped from the disclosures of the preferredembodiments described above may be combined with each other even amongdifferent preferred embodiments. Also, the components presented in therespective preferred embodiments may be combined within the scope of thepresent invention.

The preferred embodiments of the present invention are merely specificexamples used to clarify the technical content of the present invention,and the present invention should not be interpreted as being limited tothese specific examples, and the spirit and scope of the presentinvention shall be limited solely by the accompanying claims.

The present application corresponds to Japanese Patent Application No.2013-30018 filed on Feb. 19, 2013 in the Japan Patent Office, and theentire disclosure of this application is incorporated herein byreference.

REFERENCE SIGNS LIST

-   -   1 Semiconductor device    -   2 Active region    -   3 Outer peripheral region    -   4 Unit cell    -   5 Gate trench    -   6 N⁺-type source region    -   7 Source trench    -   8 P⁺-type channel contact region    -   10 Source pad    -   13 N⁻-type epitaxial layer    -   14 P-type well    -   15 N⁻-type drain region    -   16 P-type channel region    -   19 P-type layer    -   20 Gate insulating film    -   21 Gate electrode    -   22 Source trench insulating film    -   23 Trench buried layer    -   25 Surface insulating film    -   26 Outer part (of surface insulating film)    -   27 Inner part (of surface insulating film)    -   28 Contact hole    -   30 Source portion    -   41 Semiconductor device    -   42 Insulating layer    -   61 Semiconductor device    -   62 Polysilicon layer    -   81 Semiconductor device

1-29. (canceled)
 30. A semiconductor device comprising: a semiconductorlayer of a first conductivity type formed with a first trench; a gateinsulating film formed in the first trench; a gate electrode buried inthe first trench via the gate insulating film; a source region of thefirst conductivity type disposed in a manner exposed on a surface of thesemiconductor layer and contacting a first part of a side face of thefirst trench; a channel region of a second conductivity type disposed onthe source region on a back surface side relative to the semiconductorlayer, in a manner contacting the source region and a second part of theside face of the first trench; a drain region of the first conductivitytype disposed on the channel region on the back surface side relative tothe semiconductor layer, in a manner contacting the channel region and abottom face of the first trench; an active region that forms a channelin the channel region to perform a transistor operation; an outerperipheral region disposed around the active region; a source electrodeformed over the active region and the outer peripheral region, andsurface insulating films isolated in pieces in a cross sectional viewand formed over the semiconductor layer, and a thickness of at least oneof the surface insulating films over the active region from the surfaceof the semiconductor layer to a bottom of the source electrode beingthinner than thickness of some of the surface insulating films over theouter peripheral region from the surface of the semiconductor layer toan upper surface of some of the surface insulating films.
 31. Thesemiconductor device according to claim 30, further comprising: acontact hole formed in the surface insulating films, and the sourceelectrode is fulfilled in the contact hole.
 32. The semiconductor deviceaccording to claim 31, further comprising: a channel contact region ofthe second conductivity type selectively disposed on a surface siderelative to the semiconductor layer so that the channel contact regionis electrically connected with the channel region, wherein the sourceelectrode is electrically connected with the source region and thechannel contact region.
 33. The semiconductor device according to claim32, wherein cells forming the semiconductor device are structured as astripe shape.
 34. The semiconductor device according to claim 33,further comprising a gate pad formed at a region proximity to an outeredge line of the semiconductor device in a plan view.
 35. Thesemiconductor device according to claim 34, wherein the gate electrodeis a material containing poly-silicon.
 36. The semiconductor deviceaccording to claim 35, further comprising a titanium based materiallayer between the source electrode and the semiconductor layer.
 37. Thesemiconductor device according to claim 36, wherein an impurity materialforming the channel region of the second conductivity type is analuminum.
 38. The semiconductor device according to claim 36, whereinthe semiconductor layer is made of a material including SiC, GaN, ordiamond.
 39. The semiconductor device according to claim 36, wherein thethickness of the at least one of the surface insulating films over theactive region from the surface of the semiconductor layer to the bottomof the source electrode is smaller than or equal to 5000 Å.
 40. Thesemiconductor device according to claim 38, wherein the gate insulatingfilm is made of a material including SiO₂.
 41. An inverter circuitincluding the semiconductor device according to claim
 40. 42. A powermodule including the inverter circuit according to claim
 41. 43. Anelectric automotive part including the power module according to claim42.